1. Field of the Invention
The present invention relates to solid-state imaging devices and imaging apparatuses.
2. Description of the Related Art
Semiconductor image sensors, which are solid-state imaging devices, include complementary metal-oxide semiconductor (CMOS) sensors and charge-coupled devices (CCDs). The CMOS sensors include a plurality of pixels, which have photoelectric-conversion units that convert incident light to electric signals, and metal-oxide semiconductor (MOS) transistors that selectively read the electric signals from each of the pixels. The CCDs include a plurality of pixels, which have photoelectric-conversion units that convert incident light to electric signals, and transfer signal charges, which are read from each of the pixels, through a silicon substrate. Both the CMOS sensors and the CCDs are semiconductor devices in which signals are read from pixels. Recently, the CMOS sensors have drawn attention as imaging devices used in cameras for mobile phones, digital still cameras, and digital video cameras because of the positive characteristics, such as low voltage, low power consumption, and multifunctionality. The range in which the CMOS sensors are used has been expanded.
More specifically, for a color image sensor, the technology has been used in which a color filter including three colors, such as red, green, blue, is formed in each pixel (red-green-blue Bayer pattern is common) and in which color separation is spatially performed. In this technology, an excellent color reproduction can be achieved by appropriately adjusting spectral characteristics of the color filter. However, the technology has a substantial problem that it is difficult to sufficiently effectively use light that enters the color image sensor because the color filter itself considerably absorbs light. Additionally, the technology has the following problems: Since the color separation is spatially performed, it is difficult to effectively use the pixels of the color image sensor; when the number of green pixels is small, the resolution of luminance signals is decreased; and when the number of red or blue pixels is small, the resolution of color signals is decreased, or false color signals occur.
Furthermore, with the increasing miniaturization of image sensors and the increasing number of pixels in the image sensors, recently, the cell size of one pixel has been reduced to 2.0 μm square or less. In accordance with this size reduction, obviously, an area per pixel and a volume per pixel are reduced. As a result, the saturation level and the sensitivity are reduced, thereby reducing the image quality. Accordingly, if red, blue, and green signals can be obtained using one pixel, or two or three pixels without reducing the cell size, the spatial luminance and the chroma resolution can be maintained while maintaining the fixed amounts of the sensitivity and the saturation level.
In order to solve the above-described problems, recently, an image sensor in which organic-photoelectric-conversion films are used has been suggested (for example, see Japanese Unexamined Patent Application Publication No. 2003-234460). According to Japanese Unexamined Patent Application Publication No. 2003-234460, an organic-photoelectric-conversion film having a sensitivity to blue, an organic-photoelectric-conversion film having a sensitivity to green, and an organic-photoelectric-conversion film having a sensitivity to red are stacked in an order to receive light. With the configuration, blue, green and red signals can be separately obtained from one pixel, thereby improving the sensitivity. However, because it is extremely difficult to stack multiple organic-photoelectric-conversion films in view of process, the implementation of multi-layered organic-photoelectric-conversion films has not been reported. The reason for this is that the harmonization between a process for lead electrodes, which are normally metal films, and a process for the organic-photoelectric-conversion films is a serious problem, and no technology for processing the lead electrodes without damage to the organic-photoelectric-conversion films has been established.
In contrast, there are examples of a device in which light corresponding to two colors is extracted using silicon bulk spectroscopy although the number of organic-photoelectric-conversion films is one (for example, see Japanese Unexamined Patent Application Publication No. 2005-303266, and see FIG. 6 in Japanese Unexamined Patent Application Publication No. 2003-332551). However, in this device, when the difference of absorption of light with different wavelengths in a bulk of silicon is utilized, the color reproducibility is poor. For this reason, it is difficult to apply the device to a general high-resolution image sensor. Additionally, because the configuration of the device in which light corresponding to two colors is extracted through the bulk of silicon is complicated in view of process, the manufacturing cost is increased.